Blasting lance with a gas/liquid mixing chamber and a method for the expansion cooling thereof

ABSTRACT

The invention relates to a method for cooling a lance provided for converting a medium into a molten mass and/or for measuring the properties of the molten mass. A gas/liquid mixture is fed as a cooling medium into a cooling circuit which is closed up to the lance end ( 2 ) situated on the melting side. The invention provides that the gas/liquid mixture or the components thereof is/are fed and permitted to expand under pressure up to the area of the lance end ( 2 ) situated on the melting side. The invention also relates to a lance which has a mixing chamber ( 5, 6 ) connected to the cooling circuit The mixing chamber has the connections ( 3, 7 ) for a gas and liquid supply which is designed to produce the gas/liquid mixture, whereby the mixing chamber ( 5, 6 ) is connected via a pressure line ( 10 ) to at least one two-component nozzle ( 11 ) arranged in the area of the lance end ( 2 ) which is situated on the melting side.

The invention relates to a method for cooling a lance provided forintroducing a medium into a melt and/or for measuring properties of themelt.

Lances for blasting media (in particular solids and/or gases) into theinterior of metallurgical vessels such as furnaces or converters and ascarriers of instruments for measuring properties of the melt are known.They are used, for example, for oxygen-refining a pig iron melt, forblasting in media during steel treatment (for example coal for foamingthe slag) and for temperature measurement of the melt.

The end region of such a lance which faces the melt is subject to highthermal stress. From prior public use it is known to use tubular steellances, the melt-side end of which continuously burns away in operation,with the lance having to be moved up accordingly. Moreover, cooledlances with closed water cooling circuits are known. The operation ofthese lances is dangerous because, in the event of a leakage in thecooling circuit, a contact of the melt with cooling water can lead toexplosive reactions. If water is enclosed by the melt, the evaporationand expansion of the water which then take place can break up the meltin an explosive manner. Neither the chemical dissolution of the waternor a subsequent reaction of oxyhydrogen gas is to be excluded.

It has therefore already been suggested (DE 35 43 836 C2) to use twolances which are moved alternately into the operating position. Thelance located in the operating position is cooled with a gas. Because asufficient cooling action is not achieved in this way, the lance ismoved out of the furnace after a certain operating period and recooledwith water in this position which is spaced far apart from the melt.During this period the second lance continues the operation. Such analternate operation with two lances is costly.

From WO-A-92/07965 a lance is known which has a closed cooling circuitwhich is supplied with a diphase mixture.

The object underlying the invention is to create a method and a lance ofthe type named in the introduction, which make an effective and reliablelance cooling possible.

The method in accordance with the invention is characterized in that thegas/liquid mixture or its constituents is or are conducted underpressure up to and into the region of the melt-side lance end and is orare allowed to expand there.

The melt-side lance end denotes that end of the lance which, inoperation, faces the melt or optionally dips into it. It is thethermally highly stressed lance end. The cooling circuit is closedtowards the melt-side lance end. In this region no exit of coolant takesplace, the coolant instead being returned into a region of the lancewhich is spaced apart from the melt and exiting the lance at that place.The coolant circuit as a whole can either be completely closed, but anopen cooling circuit can also be used, where the heated cooling medium,exiting the lance and spaced apart from the melt-side end, is notreused.

The gas content of the mixture used in accordance with the invention ispreferably air or an inert gas (for example nitrogen or argon), theliquid content preferably water.

The gas/liquid mixture is conducted in accordance with the inventionunder pressure up to and into the region of the melt-side lance end. Theterm “region of the melt-side lance end” denotes a region lying in thevicinity of the appropriate lance end, which region is already thermallyhighly stressed in operation. The pair of terms “conducting underpressure up to and into the region of this end and the subsequentallowing of expansion” is to be understood to mean that in the namedregion a sudden pressure drop of the gas/liquid mixture takes place.Accordingly, the realization of the invention only depends on anappropriate pressure difference, not on the absolute levels of therespective pressures. Allowing expansion (preferably by way of allowingexit from an appropriate nozzle into an area of less pressure) has theeffect that the liquid phase of the mixture is broken up into finedroplets and/or evaporated. Both effects substantially increase thecooling power because, on the one hand, the evaporating requiresconsiderable quantities of heat and, on the other hand, finely broken-updroplets as a result of their large surface can remove additional heatquickly and effectively (with evaporation). The expansion, provided inaccordance with the invention, of the coolant mixture in the region ofthe melt-side lance end therefore effects a clear increase of thecooling power in comparison with the prior art. On the other hand, itensures a clear increase of safety because, as a result of the expansionprocedure in the region of this lance end, there is little or no liquidphase. In the event of operating disturbances, melt penetrating intothis region can therefore not enclose larger quantities of water andthereby cause thermal explosions. Within the scope of the invention, thediphase mixture of gas and liquid can be produced spaced apart from themelt-side lance end and can be supplied as finished mixture underpressure to this end and allowed to expand there. It is likewisepossible to conduct gas and liquid separately under pressure up to andinto the region of the melt-side lance end and either to only mix themwith each other shortly before the expansion procedure or, on the otherhand, to allow them to expand by way of separate nozzles which arearranged in such a way that the gas/liquid mixture is produced in situduring the expansion procedure. For example, separate nozzles can bearranged in such a way that exiting liquid is drawn off by the expandinggas and is broken up to form a fine aerosol.

The method in accordance with the invention requires considerablysmaller quantities of liquid for cooling than the water cooling known inthe prior art. The gas/liquid flow is adjusted in such a way that theliquid content in the region of the thermally particularly stressedmelt-side lance end evaporates for the most part or completely as aresult of the expansion. This has two advantages. Firstly, in this wayfor cooling, not only is the thermal capacity of the liquid (of thewater) used, but also the substantially greater evaporation heat for thephase transition liquid-vapour, and even with relatively small liquidflows a high cooling power is obtained. If, in the event of operatingdisturbances, in the region of the melt-side end there results a leakagein the coolant line, the large surface of the gas/liquid mixturesupplied as aerosol has the effect that in any case there results a veryrapid evaporation of the liquid content, even before the melt canenclose drops of liquid.

The liquid portion of the cooling medium used in accordance with theinvention is usually water. If operating conditions are chosen where thewater content in the region of the melt-side lance part evaporates forthe most part or completely, the cooling circuit is preferably suppliedwith demineralized water in order to avoid calcareous deposits in thecorresponding region of the cooling area. If demineralized water is notavailable and if the cooling circuit must be supplied with usual tapwater or untreated water, the gas/liquid flow is preferably adjusted insuch a way that a smaller portion of the water evaporates in the regionof the melt-side lance end, the rest being retained as finelydistributed aerosol. Unwanted calcareous deposits are in this waylargely avoided.

The flow speed of the diphase mixture, which is high as a result of theexpansion procedure, does not entrain evaporated water, with the resultthat no stationary water can collect in the region of the lance tip,which water could lead to a danger of explosion in the event of a meltpenetration.

The gas/liquid mixture can be produced outside the lance and supplied tothe lance already as a mixture. However, within the scope of theinvention it is preferred that the lance has a mixing chamber connectedto the cooling circuit, the mixing chamber having connections for a gasand liquid supply and being constructed for the production of agas/liquid mixture. The mixing chamber is arranged spaced apart from themelt-side lance end. It is preferably located in the part of the lanceprojecting out of the furnace or converter.

The gas/liquid mixture is conducted from the mixing chamber preferablyat a pressure of 2 to 6 bar, then preferably about 3 bar, through apressure pipe towards the melt-side lance end. In the region of this enda two-component nozzle is arranged, from which the mixture expands intoa cooling area arranged in the region of the lance tip. Within the scopeof the invention, the term “two-component nozzle” denotes any devicewhich allows a passage of a liquid/gas mixture and, in the process, canmaintain a pressure difference between supply side and exit side in sucha way that a nozzle action results, that is to say a division of thesupplied mixture in the region of lower pressure lying after the nozzle.Upon exit from the nozzle, the liquid content of the mixture is brokenup into fine droplets. The expanded and heated mixture is conducted awayfrom the melt-side lance end by way of a second pipe and exits the lanceagain at a connection which is preferably arranged outside theconverter. The pressure of the mixture after exit from the two-componentnozzle or nozzles lies preferably somewhat above atmospheric pressure.If the lance is used in a dipping operation it should be greater thanthe counterpressure of the liquid melt surrounding the lance tip. If, asa result of operating disturbances, there results a melting of the lancetip and a penetration of melt into the cooling area, the excess pressureprevailing therein prevents the further penetration of melt and possiblyslag.

Advantageously, the mixing chamber has two annular chambers which areconcentric to each other and surround the lance tube, in the radialdividing wall of which annular chambers connection bores or connectionopenings are arranged. The term lance tube denotes the inner tube of theentire lance arrangement, which is provided for the introduction of gasand/or solids into the melt. The inner annular chamber can receivewater, for example from its end face, the outer annular chamberreceiving compressed air from the circumference. By way of the bores inthe radial dividing wall compressed air is mixed into the water. Themixture produced is removed at the melt-side end face of the mixingchamber and carried away.

The pressure pipe for connecting mixing chambers and a two-componentnozzle is preferably a closed circular pipeline which surrounds thelance tube concentrically. The return of the expanded mixture from themelt-side lance end likewise preferably takes place by way of a closedcircular pipeline which can be constructed as a second closed circularpipeline which surrounds the pressure pipe concentrically.

A second embodiment of a lance in accordance with the invention hasseparate pressure pipes for the supply of gas, on the one hand, andliquid, on the other hand, towards the melt-side lance end. Thesepressure pipes can be constructed as closed circular pipelines whichsurround the lance tube concentrically. In the region of the melt-sidelance end the pressure pipes end in nozzle arrangements, from which gas,on the one hand, and liquid, on the other hand, exit and, in theprocess, in situ, that is to say during the expansion procedure, mix toform a fine-particle aerosol. The suction action of the expanding gasentrains exiting liquid and divides it into fine droplets. The flowspeed of the aerosol produced in situ is so high that no considerablequantities of water whatever remain in the region of the melt-side lanceend. There is therefore no, or only a small, safety risk in the event ofa penetration of melt. The operating pressures of this lance can lieclearly below 3 bar. The necessary excess pressure in the gas line(compressed air line) amounts to, for example, 1 to 2 bar, preferablyabout 1.5 bar. The liquid (water) only needs to be supplied at a lowexcess pressure of below 1 bar, preferably about 0.5 bar, because duringthe aerosol formation it is entrained by the expanding compressed airand is divided.

A preferred field of use of the invention is the treatment of, or theperformance of measurements on, metallurgical melts, for example pigiron or steel melts. However, the invention is not restricted to usewith metal melts, but can be used for additional melt flows of hightemperature (for example glass melts).

Exemplary embodiments of the invention will be explained in thefollowing with reference to the drawings.

FIG. 1 shows a longitudinal section through a lance in accordance withthe invention.

FIG. 2 shows a cross section along the plane A—A of FIG. 1.

FIG. 3 shows a longitudinal section through a second embodiment of alance in accordance with the invention.

FIG. 4 shows a cross section along the plane A—A of FIG. 3.

The lance in accordance with the invention according to FIGS. 1 and 2has an inner lance tube 1, through which solids and/or gases of the meltare supplied. The exit of these media into the melt takes place at themelt-side lance end 2. The lance tube 1 is surrounded by a coolingdevice which is described in more detail in the following.

By way of a connection piece 3, cooling water is supplied to an annularchamber 4 which surrounds the lance tube 1. The end faces of the annularchamber 4 and of the inner chamber 5 of the axially connecting mixingchamber are connected to each other, with the result that this innerannular chamber 5 is supplied with water from the annular chamber 4. Theinner annular chamber 5 is surrounded by an outer annular chamber 6which is supplied with compressed air by way of a connection piece 7.The two annular chambers 5, 6 together form the mixing chamber. Theradial dividing wall 8 between the annular chambers 5 and 6 hasconnection bores indicated at 9. Compressed air and water mix with eachother and the mixture is conducted through the closed circular pipeline(pressure pipe) 10, connecting axially into the inner annular chamber 5,towards the melt-side lance end. The pressure of the mixture in thepressure pipe 10 amounts to about 3 bar.

The closed circular pipeline 10 is formed in the region of the melt-sideend 2 of the lance into six two-component nozzles 11 distributed evenlyover the lance circumference. The water/air mixture expands upon exitfrom the two-component nozzles into the annular cooling area 12. Thewater is broken up into very fine droplets by this expansion procedure.The large surface of the water supplied favours a rapid heat absorptionand therefore a high cooling power. The forming of the closed circularpipeline 10 into six two-component nozzles 11 allows operation of thelance with tap water or process water as a constituent of the coolingmedium. The inside diameter of the two-component nozzles 11 makes thepassage of impurities and particles possible, the latter possibly beingcontained in the process water. If the lance is to be operatedexclusively with demineralized water, the closed circular pipeline 10can be narrowed in the region of the cooling chamber of the cooling area12 to form an annular gap with an inside diameter of about 0.5 mm, withthe annular gap surrounding the lance tube 1 in a rotationallysymmetrical manner. This annular gap forms a single two-componentnozzle. The forming of several discrete two-component nozzles 11 is notnecessary in this case.

At the opposite (melt-side) end face of the cooling chamber 12 themixture exiting from the two-component nozzles 11 meets a curved coolingsurface 13, by way of which its direction of movement is deflected andit is supplied to the coolant removal line constructed as second closedcircular pipeline 14. The water content of the mixture suppliedevaporates in the cooling chamber 12 preferably completely. Inparticular operating conditions, if unusually high temperatures resultin the cooling chamber 12, the cooling action can possibly be supportedby the greatly endothermic division of a portion of the water intomolecular hydrogen and oxygen.

If, in the event of operating disturbances, the lance burns away in theregion of the melt-side end 2 and the cooling chamber 12 opens towardsthe melt, as a result of the use of the fine aerosol as cooling mediumthere is practically no danger that water which is still liquid will beenclosed by the melt and will subsequently evaporate in an explosivemanner. In the cooling area 12 an excess pressure is preferably set,which, during dipping operation of the lance, is sufficient in order toforce back molten metal or slag which is possibly penetrating into thecooling chamber 12 and in order to prevent a further penetration.

The cooling medium flowing back through the closed circular pipeline 14is removed from the lance by way of an annular chamber 15 and aconnection piece 16. It can either be discarded (open cooling circuit)or, on the other hand, returned anew into the cooling circuit.

The annular chamber 15 has a second connection 17 which is connected toa safety pressure-control valve, not shown in the drawing.

Apart from being used to introduce media into the melt, the lance canalso be used to measure properties of the melt. For this purpose,measuring instruments can be arranged in the region of the melt-side end2, the measuring instruments not being shown in the drawing. Forexample, the temperature of the melt can be measured by a radiationpyrometer. With a steel melt, a multi-element analysis can be carriedout, for example by means of laser-induced emission spectroscopy. Inthis way, for example, a steel refinement process can be carried outmetrologically and ended in the desired state.

To perform such measurements the lance is guided with the measuringinstrument arranged thereon into the region of the surface of the steelbath. Preferably compressed air or an inert gas such as nitrogen isblasted through the lance tube 1, which, on the one hand, keeps thelance opening clear, and, on the other hand, frees the steel bathsurface of slag.

The lance in accordance with the invention is introduced through anopening in the wall or cover into the converter or furnace. Theconnections for the supply and removal of the cooling media and themixing chamber are preferably located outside the converter in anappropriately cooler region.

FIGS. 3 and 4 show a second embodiment of the invention, where gas andliquid are conducted separately up to the melt-side lance end 2 andwhere the gas/liquid mixture is produced during the expansion procedureonly in situ. Here, the same reference numerals denote functionallyidentical components in comparison with the embodiment according toFIGS. 1 and 2.

The substantial difference compared with the embodiment according toFIGS. 1 and 2 consists in that three closed circular pipelines,concentric to each other, are arranged around the inner lance tube 1.The inner closed circular pipeline 18 conducts cooling water to themelt-side lance end 2, being connected to the annular chamber 4 for thispurpose. The middle closed circular pipeline 19 is supplied withcompressed air by way of the connection 7 and the annular chamber 6provided with connection bores 9. As in the first embodiment, the outerclosed circular pipeline 14 is used to return the heated cooling mediumto the annular chamber 15 and the associated connection 16.

Water and gaseous medium (compressed air) flow through the closedcircular pipelines 18, 19 separately to the melt-side lance end 2. Uponthe exit of the compressed air into the annular chamber 12 and theaccompanying expansion, it likewise entrains exiting cooling water anddivides it to form a fine aerosol. The diphase mixture used inaccordance with the invention is produced in situ.

Surprisingly, the operating pressure of this embodiment can be clearlyreduced compared with the lance according to FIGS. 1 and 2. Therefore,to achieve a fine-particle aerosol, which passes through the annularchamber 12 at a high flow speed and is subsequently removed, it issufficient to supply the water in the closed circular pipeline 18 at anexcess pressure of 0.5 bar and the compressed air in the closed circularpipeline 19 at an excess pressure of 1.5 bar.

What is claimed is:
 1. Method for cooling a lance having a melt sideend, a tube for introducing a medium into a melt and for measuringproperties of the melt, a closed cooling circuit integral with saidmelt-side lance end (2) and tube therein, with a gas/liquid mixtureconducted as a cooling medium, characterized in that the gas/liquidmixture or its constituents are conducted under pressure up to and intosaid closed cooling circuit integral with melt-side lance end (2) andallowed to expand there.
 2. Method according to claim 1, characterizedin that the gas/liquid mixture is produced in a mixing chamber (5, 6) ofthe lance which is arranged spaced apart from the melt-side lance end(2).
 3. Method according to claim 1, characterized in that thegas/liquid mixture is conducted under a pressure substantially of 3 bar,to the melt-side lance end (2).
 4. Method according to claim 1,characterized in that gas and liquid are conducted separately to themelt-side lance end (2) and are allowed to expand there, wherein duringthe expansion procedure a gas/liquid mixture is produced in situ. 5.Lance for carrying out the method according to claim 2, with a closedcooling circuit integral with the melt-side lance end (2), wherein amixing chamber (5,6) is arranged which is spaced apart from themelt-side lance end (2) and connected to the cooling circuit, the mixingchamber having connections (3, 7) for a gas and liquid supply and beingconstructed for producing a gas/liquid mixture, wherein the mixingchamber (5, 6) is connected by way of a pressure pipe 10 to at least onetwo-component nozzle (11) arranged in the region of the melt-side end(2) of the lance.
 6. Lance according to claim 5, wherein the mixingchamber (5, 6) has two annular chambers (5, 6) which are concentric toeach other and surround said lance tube, with connection bores (9) beingarranged in the radial dividing wall (8) of said annular chambers. 7.Lance according to claim 6, characterized in that the pressure pipe is aclosed circular pipeline (10) which surrounds the lance tube (1)concentrically.
 8. Lance according to claim 7, characterized in that, toreturn the expanded gas/liquid mixture from the melt-side lance end (2)to the outlet (16) of the mixture out of the lance, a second closedcircular pipeline (14) is provided, which surrounds the pressure pipe(10) concentrically.
 9. Lance for carrying out the method according toclaim 4, with a cooling circuit closed towards the melt-side lance end(2), characterized by two pressure pipes (18, 19) connected toconnections (3, 7) for a gas and liquid supply, the pressure pipes beingconstructed for the separate supply of gas, on the one hand, and liquid,on the other hand, towards the melt-side lance end (2) and ending in theregion of the melt-side lance end (2) in nozzle arrangements, by way ofwhich a gas/liquid mixture is produced in situ.
 10. Lance according toclaim 9, characterized in that the pressure pipes are closed circularpipelines (18, 19) which surround the lance tube (1) concentrically.